Geological Society of London. ovo 
II.—June 19, 1889. —Prof. J. W. Judd, F.R.S., Vice-President, in 
the Chair.—The following communications were read :— 
1. “On Tachylyte from Victoria Park, Whiteinch, near Glasgow.” 
By Frank Rutley, Esq., F.G.S. 
This paper dealt with the microscopic characters of certain thin 
tachylytic selvages occurring on the margins of white-whin (basalt) 
veins which traverse Carboniferous shales in Victoria Park, and 
which have already been described in some detail by Messrs. John 
Young and D. Corse Glen. The white-whin veins, which sometimes 
are not more than an inch in breadth, are found to become gradually 
more vitreous in passing from the middle to the sides of the veins. 
Near the margin they become densely spherulitic, the spherulitic 
band on either side of the vein being followed by a less spherulitic 
and more glassy band, the vitreous matter of which appears nearly 
or quite colourless. A sharp but irregular boundary-line follows, 
beyond which lies a band of a more or less deep brown or coffee- 
coloured glass, which the author considers to have resulted from the 
fusion of the shale, two narrow vitreous bands of different origin 
being thus developed side by side on each side of the vein, the 
colourless bands representing the chilled margins of the vein, the 
brown bands the fused surfaces of the walls of shale. The author 
only suggested this as a plausible explanation of the microscopic 
phenomena. An analysis of portion of one of these whin veins with 
its adherent tachylyte, made by Mr. Philip Holland, was appended 
to the paper. 
2. “The Descent of Sonninia and of Hammatoceras.” By 8. 8. 
Buckman, Esq., F'.G.S. 
The author reviewed the history and literature of the genus 
Sonninia, Bayle, which was founded to receive the Ammonites of the 
Sowerbyi-group, formerly classed, together with those of the Insignis- 
group, in the genus Hammatoceras. 
The reasons why the genus Sonninta is not descended from 
Hammatoceras, or from Haugia (Variabilis-group), were set forth. 
Then, proceeding to trace out the life-history of Plewroceras, Amal- 
theus, and Sonninia, as shown by their inner whorls, the author 
arrived at the conclusion that these three genera were descended from 
a common source, and that they form three branches from one stem. 
The development of the genus Hammatoceras, sensu stricto, was 
then traced out, and its descent shown to be from the genus Deroceras, . 
which is in accordance with the general ideas upon the subject. 
The difference in the descent of Sonninia and Hammatoceras was 
taken to justify the separation of the former from the latter. The 
genus Sonninia would be correctly placed in the family Amaltheide ; 
while the genus Hammatoceras would be placed in the same family 
as Stephanoceras. 
Of the numerous new species belonging to the genera Sonninia 
and Hammatoceras, certain forms, necessary to elaborate the ideas 
set forth above, were described and definitely separated. The paper 
also touched upon certain other facts connected with Hammatoceras, 
Sonninia, and cognate genera. 
